The present application claims priority of Japanese patent application 82/220816 filed Dec. 15, 1982.
The present invention relates to a silicone sealant composition, and more particularly pertains to a silicone sealant composition which does not stain the circumference of a joint when used as a sealant for joint parts of building structures.
Polyorganosiloxane compositions which can be cured at room temperature to form a rubbery elastomer are widely used as construction sealants since they have excellent resistance to heat and weather and are relatively free of changes in physical properties due to extreme temperature or exposure to ozone or ultraviolet light.
These polyorganosiloxane compositions have excellent characteristics as mentioned above, but they have the disadvantage that not all of the polyorganosiloxane participates in crosslinking, that is, even after curing some is left behind, hence the circumference of a joint is stained by the exudation thereof.
Therefore, there are disadvantages that since dust is liable to be deposited on the surface of the joint where the polyorganosiloxane exudes and spreads, such dust adheres to the polyorganosiloxane and is also rendered water-repellent. Accordingly, the dust cannot be washed off by rain water and staining around the joint proceeds causing the beauty of the structure to be spoiled.
There has been proposed a method for preventing the circumference of the joint from being stained in Japanese Patent Laid-Open No. 102343/1982, wherein a polyorganosiloxane composed of SiO.sub.2 units and R.sub.3.sup.1 SiO.sub.178 units and containing silanol groups attached to the silicon atoms, in which R.sup.1 is the same or different substituted or unsubstituted monovalent hydrocarbon groups, a silanol group-terminated polyorganosiloxane and a silicon compound containing organoaminoxy groups attached to the silicon atoms are dissolved in a volatile organosiloxane and an organic solvent, and the surface of a silicone sealant composition is coated therewith and cured to form a polysiloxane film on the surface of said sealing material composition, whereby polysiloxane which does not participate in crosslinking is prevented from exuding and spreading around the joint by the polysiloxane film.
The degree of staining around the joint can be considerably reduced by this method. However, since the film formed on the surface of the silicone sealant composition has good compatibility with the polyorganosiloxane exuding, it is impossible to completely prevent the polyorganosiloxane from exuding. Therefore, this method is not considered to be a preferred method.
The present applicant has developed a silicone sealant composition which is free from the disadvantages associated with conventional methods, and has found that the above mentioned disadvantages can be eliminated by incorporating a small amount of an ultraviolet-curable oligomer containing acryl groups in a polyorganosiloxane composition.
The present invention is based on this finding. An object of the present invention is to provide a silicone sealant composition which does not stain the circumference of the joint.